1. Field of the Invention
This invention relates to an apparatus and process for extruding plastic materials including mixtures of plastic materials, additives, dyes and the like in one step, and more particularly is concerned with an extruder screw for processing mixtures of plastic material and other components utilizing a low shear, discrete dispersive type mixing into final finished products.
2. Description of Prior Art
Mixing a fluid or plastic mass with modifying agents, additives and the like to produce a homogeneous material is typically carried out by mixing apparatuses in various forms known to those skilled in the art. Typically, a conventional extruder screw and barrel apparatus is employed either separately or in conjunction with static flow diverting means. These conventional mixers and extruders are all shear dependent in that flow of plastic material may become channelized with hotter, less viscous material tending to run in channels along the central axis of the extruder section and cooler, more viscous material tending to adhere to portions of the extruder barrel at some points.
For example, with a conventional extruder screw having twenty-four turns, only 80% of the material may be melted by the first twelve turns while the remaining twelve turns produce only a 95% melt. In this case, the more viscous or unmelted material is torn away from the barrel and swept into the die in which forming is to take place. To prevent this, more heating and pressure is applied through the extruder screw resulting in an excessive use of energy and undesirable increase in temperature of material in the barrel, which temperature increase can degrade some portions of the material. Thus, there is a need for an apparatus which is capable of providing a more complete melting and mixing so as to provide a homogeneous molded end product.
U.S. Pat. No. 4,447,156 to Csongor teaches a modular mixing apparatus providing laminar displacement of a fluid mass which is thereafter guided along undulating linear paths of travel of relatively short axial length, which material thereafter undergoes further laminar displacement, which provides a high degree of intimate mixing and blending. The apparatus includes a main shaft which is engaged with a threaded end of an extruder screw and rotatable therewith, spaced apart shear ring elements rotatable with the shaft, and a stationary shearing control sleeve which is located between the shear ring elements disposed around the driver shaft, and fixed to an outer extruder barrel component of the apparatus. See also U.S. Pat. No. 4,697,928 and U.S. Pat. No. 4,749,279, both to Csongor, and both teaching a similar apparatus.
U.S. Pat. No. 2,765,491 to Magerkurth teaches a screw type extruder apparatus for mixing different materials such as rubber particles, oils, and chemicals without employing severe crushing, shearing, or mastication action. U.S.
Pat. No. 4,408,887 to Yamaoka teaches a continuous kneader employing a rotary screw shaft rotatable within a cylinder for transporting a fluid axially thereof, rotary discs mounted on the shaft having radial projections and recesses alternately arranged on each side surface thereof, and fixed discs on the cylinder and arranged on the opposite sides of each rotary disc coaxially therewith. An extrusion apparatus for mixing and extruding thermoplastic and rubberlike materials having a rotor member rotatable within the bore of a barrel member is taught by U.S. Pat. No. 5,348,388 to Geyer. U.S. Pat. No. 3,836,127 to Csongor teaches an apparatus for extruding plastic materials having an extruder screw for forming a melted mass which is moved in a helically-directed stream and, at a predetermined point, includes flow diverting means so as to abruptly change the flow pattern. U.S. Pat. No. 3,486,192 to Le Roy teaches an apparatus for the controlled degradation of resinous thermoplastic materials in which the molten resinous material is passed through an extrusion apparatus having at least one special cylindrical or tapered cylindrical circumferential shearing section in the extruder screw arrangement. Input grooves are arranged extending substantially longitudinally in the surface of the special section with groove openings at the input, which grooves terminate in dead ends before reaching the output end of the section. Output grooves arranged between the input grooves extend substantially longitudinally in the surface of the screw section with openings at the output end which terminate in dead ends before reaching the input end of the section. As the section rotates, plastic material is fed under pressure from a prior stage into the input grooves and shears over lands between the grooves thereby shearing the plastic, after which it is passed into the output grooves, through the output openings and into the next conveyor stage. Finally, U.S. Pat. No. 5,409,366 to Vincent teaches a screw processor having means for controlling the generation of shear within the apparatus comprising a housing having at least one screw mounted on a shaft for rotation therein which produces a substantially uniform mix as the material is transported from an inlet to the outlet and a shear force generating device associated with the screw or shaft and located in the region of the outlet, the shear force generating device forming a gap through which material is forced by the screw to exit from the housing, whereby the shearing force applied to the material during passage through the apparatus is concentrated in the shear generating device.